U.S. patent number 7,923,190 [Application Number 12/578,112] was granted by the patent office on 2011-04-12 for toner.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Tadashi Dojo, Shuichi Hiroko, Michihisa Magome, Takashi Matsui, Akira Sakakibara, Tomohisa Sano, Eriko Yanase.
United States Patent |
7,923,190 |
Magome , et al. |
April 12, 2011 |
Toner
Abstract
In a toner containing at least a binder resin, a colorant, an
ester compound and a low-melting material, the ester compound is an
ester of dipentaerythritol with a carboxylic acid having 18 or more
to 25 or less carbon atoms, and, where the melting point of the
ester compound is represented by Tm.sub.(A) (.degree. C.) and the
melting point of the low-melting material is represented by
Tm.sub.(B) (.degree. C.), the toner satisfies the relationship of:
Tm.sub.(B).ltoreq.Tm.sub.(A)+5.
Inventors: |
Magome; Michihisa (Mishima,
JP), Dojo; Tadashi (Numazu, JP), Yanase;
Eriko (Kawasaki, JP), Matsui; Takashi
(Suntou-gun, JP), Sano; Tomohisa (Suntou-gun,
JP), Sakakibara; Akira (Susono, JP),
Hiroko; Shuichi (Susono, JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
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Family
ID: |
41377209 |
Appl.
No.: |
12/578,112 |
Filed: |
October 13, 2009 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100028795 A1 |
Feb 4, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/JP2009/059941 |
May 26, 2009 |
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Foreign Application Priority Data
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May 28, 2008 [JP] |
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2008-139237 |
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Current U.S.
Class: |
430/108.4;
430/108.8; 430/111.4 |
Current CPC
Class: |
G03G
9/09733 (20130101); G03G 9/08793 (20130101); G03G
9/083 (20130101); G03G 9/0827 (20130101); G03G
9/08755 (20130101); G03G 9/08782 (20130101); G03G
9/08711 (20130101) |
Current International
Class: |
G03G
9/08 (20060101) |
Field of
Search: |
;430/109.3,109.4,108.8,111.4,108.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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11-218960 |
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Aug 1999 |
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JP |
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2000-019768 |
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Jan 2000 |
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JP |
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2001-147550 |
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May 2001 |
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JP |
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2002-072540 |
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Mar 2002 |
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JP |
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2002-072546 |
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Mar 2002 |
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JP |
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2002-221814 |
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Aug 2002 |
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JP |
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2004-361983 |
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Dec 2004 |
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JP |
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2006-078981 |
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Mar 2006 |
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JP |
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2006-098745 |
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Apr 2006 |
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JP |
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WO 98/20396 |
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May 1998 |
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WO |
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WO 01/01200 |
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Jan 2001 |
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WO |
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Other References
English Langauge machine translation of JP 4106873 B (Jun. 2008).
cited by examiner .
English language machine translation of JP 11-002922 A (Jan. 1999).
cited by examiner .
International Preliminary Report on Patentability dated Jan. 20,
2011, in International Application No. PCT/JP2009/059941. cited by
other.
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Primary Examiner: RoDee; Christopher
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of International Application No.
PCT/JP2009/059941 filed May 26, 2009, which claims the benefit of
Japanese Patent Application No. 2008-139237, filed May 28, 2008.
Claims
What is claimed is:
1. A toner which comprises toner particles containing at least a
binder resin, a colorant, an ester compound and a low melting
material; the ester compound being an ester of dipentaerythritol
with a carboxylic acid having 18 or more to 25 or less carbon
atoms; where the melting point of the ester compound is represented
by Tm.sub.(A)(.degree. C.) and the melting point of the low melting
material is represented by Tm.sub.(B)(.degree. C.), the toner
satisfying the relationship of: Tm.sub.(B)<Tm.sub.(A); wherein
the ester compound has a solubility S(A) in a styrene acrylic
resin, of 2.5% or less, the styrene-acrylic resin has a glass
transition temperature of 54.0.degree. C..+-.1.0.degree. C., a
number-average molecular weight of 20,000.+-.2,000 and a weight
average molecular weight of 200,000.+-.20,000; and wherein the low
melting material has a solubility S(B) in the styrene acrylic
resin, of from 5.5% or more to 20.0% or less, and S(A)<S(B).
2. The toner according to claim 1, wherein the ester compound has a
solubility S(A) in a styrene acrylic resin, of 2.0% or less.
3. The toner according to claim 1, wherein the ester compound has a
solubility in a styrene monomer at 40.degree. C., of less than 5.0%
by mass.
4. The toner according to claim 1, wherein the toner particles
contain the ester compound in an amount of from 3.0 parts by mass
or more to 20.0 parts by mass or less, based on 100 parts by mass
of the binder resin.
5. The toner according to claim 1, wherein the low melting material
is in a content from 1.2 times or more to 3.0 times or less the
content of the ester compound by mass.
6. The toner according to claim 1, wherein the ester compound has a
melting point of from 70.degree. C. or more to 90.degree. C. or
less.
7. The toner according to claim 1, which has an average circularity
of 0.950 or more.
8. The toner according to claim 1, wherein a binder resin component
of the toner has THF-insoluble matter in a content of from 5.0% by
mass or more to 65.0% by mass or less.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a toner used in recording processes
utilizing electrophotography, electrostatic recording, magnetic
recording or toner jet recording.
2. Description of the Related Art
A number of methods are conventionally known as methods for
electrophotography. In general, copies or prints are obtained by
forming an electrostatic latent image on an electrostatically
charged image bearing member (hereinafter also termed
"photosensitive member") by utilizing a photoconductive material
and by various means, subsequently developing the latent image by
the use of a toner to form a toner image as a visible image,
further transferring the toner image to a recording medium such as
paper as occasion calls, and then fixing the toner image onto the
recording medium by the action of heat and/or pressure. Apparatus
for such image formation include copying machines, printers and so
forth.
These printers or copying machines are being changed over from
analogue machines to digital machines, and it is strongly sought to
have a good reproducibility of latent images and a high resolution
and at the same time to be made high-speed and reduce power
consumption in their use. Here, take note of printers, for example.
The proportion of power consumption in the fixing step is fairly
large in respect to the total power consumption, and hence the
power consumption may increase with a rise in fixing temperature. A
high fixing temperature may also cause problems such as curl of
image-printed paper after fixing. Accordingly, there is a great
desire for making fixing temperature lower.
Meanwhile, there is also a great desire for on-demand performance
in printers and copying machines, and, in recent years, what is
called a film fixing assembly and a magnetic induction type fixing
assembly have been brought forth. These fixing assemblies have a
very good on-demand performance. However, it is the case that,
compared with conventional heat roller type fixing assemblies,
pressure is applicable with difficulty to make the fixing
performable with greater difficulty.
Further, printers need to deal with a variety of recording
materials, and hence there is a great desire for a toner having a
good fixing performance in a broad temperature region. Also, the
printers or copying machines, which are sought to reduce power
consumption, are on the other hand being made more high-speed,
where the toner is also required to be improved in running
stability.
To cope with the above, many studies have been made on how toners
are made fixable at a low temperature, and it is reported that the
use of a polyfunctional ester wax enables improvement in
low-temperature fixing performance (see Japanese Patent Laid-open
Applications No. 2000-019768 and No. 2006-098745 and International
Publication WO98/20396).
A toner is also proposed which makes use of a polyfunctional ester
wax having a specific solubility in styrene monomers and a specific
molecular weight, and it is reported that the toner has superior
low-temperature fixing performance and images with a high
resolution are obtainable (see International Publication WO01/01200
and Japanese Patent Laid-open Application No. 2001-147550).
It is further reported that the use of two types of waxes in
combination enables improvement in low-temperature fixing
performance (see Japanese Patent Laid-open Applications No.
H11-218960, No. 2002-072540 and No. 2002-072546).
However, even with use of such toners, it has not well been
succeeded in achieving both the on-demand performance and the
low-temperature fixing performance, and it has been insufficient to
be adaptable to high-speed processing. Moreover, there has been
room for much further improvement also in respect of image
stability during long-term service.
SUMMARY OF THE INVENTION
The present invention has been made taking account of the above
problems the background art has had. Accordingly, an object of the
present invention is to provide a toner which has superior
low-temperature fixing performance and can enjoy a high image
density without causing any fog even during long-term service.
The present invention provides a toner having toner particles
containing at least a binder resin, a colorant, an ester compound
and a low-melting material; the ester compound being an ester of
dipentaerythritol with a carboxylic acid having 18 or more to 25 or
less carbon atoms; and where the melting point of the ester
compound is represented by Tm.sub.(A) (.degree. C.) and the melting
point of the low-melting material is represented by Tm.sub.(B)
(.degree. C.), the toner satisfying the relationship of:
Tm.sub.(B).ltoreq.Tm.sub.(A)+5.
According to the present invention, it can have superior
low-temperature fixing performance and can enjoy a high image
density without causing any fog even during long-term service.
Further features of the present invention will become apparent from
the following description of exemplary embodiments with reference
to the attached drawing.
BRIEF DESCRIPTION OF THE DRAWING
The FIGURE is a diagrammatic sectional view showing an example of
an image forming apparatus in which the toner of the present
invention is favorably usable.
DESCRIPTION OF THE EMBODIMENTS
Preferred embodiments of the present invention will now be
described in detail in accordance with the accompanying
drawings.
As a result of studies made by the present inventors, it has turned
out that the use of an ester compound of dipentaerythritol with a
carboxylic acid having 18 or more to 25 or less carbon atoms in
combination with a low-melting material and the controlling of the
melting points of the both enables the toner to have superior
on-demand fixing performance, have very good low-temperature fixing
performance and enjoy a high image density without causing any fog
even during long-term service. Thus, they have accomplished the
present invention.
First, regarding the ester compound used in the present invention,
components constituting the ester compound are dipentaerythritol
and a long-chain carboxylic acid having 18 or more to 25 or less
carbon atoms, which are very bulky. Hence, the ester compound may
soak into the binder resin with difficulty even though it has
melted by heat applied at the time of fixing, so that, if such an
ester compound is used alone, it can not bring out any sufficient
plasticizing effect to make any good fixing performance
achievable.
However, such an ester compound and a low-melting material that
satisfies the relationship of Tm.sub.(B).ltoreq.Tm.sub.(A)+5 where
the melting point of the ester compound is represented by
Tm.sub.(A) (.degree. C.) and the melting point of the low-melting
material is represented by Tm.sub.(B) (.degree. C.) are used in
combination. In such a case, the toner can be very improved in its
low-temperature fixing performance. As to the reason therefor, the
present inventors consider it as explained below:
As stated above, the ester compound as used in the present
invention may soak into the binder resin with difficulty even
though it has melted by heat applied at the time of fixing.
However, since it does not soak into the binder resin even though
it has melted, toner particles are considered to stand closely in
liquid-at-core structure (being so structured as to be liquid at
cores) in their interiors. In such a case, although the ester
compound does not soak out of the toner particles, the toner
particles are considered to stand readily deformable by pressure
acting from the outside at the time of fixing.
In addition, the ester compound in the present invention is, as
being highly bulky, considered to come to more increase in volume
than other compounds when it melts. Hence, any pressure acting from
the interiors of toner particles increases to make them stand
deformable with ease as toner particles, as so considered.
In the present invention, it is essential to use the low-melting
material (what is called wax) that satisfies the relationship of
Tm.sub.(B).ltoreq.Tm.sub.(A)+5. The use of such a low-melting
material and the ester compound in combination enables achievement
of a very good low-temperature fixing performance for the first
time.
This is because the ester compound has a melting point closed to
that of the low-melting material (or the low-melting material has a
lower melting point than the former). Thus, it follows that the
ester compound melts at the time the ester compound and the
low-melting material have substantially simultaneously melted or
the low-melting material has melted, so that a good releasability
can be achieved which is good for the ester compound to push out
the low-melting material. Further, since the ester compound may
soak into the binder resin with difficulty, toner particles come to
stand closely in liquid-at-core structure, so that the toner
particles can be deformed by pressure acting from the outside at
the time of fixing to promise good anchoring to recording mediums,
as so considered. Here, in the toner of the present invention, it
is preferable that the ester compound and the low-melting material
are enclosed in the binder resin to have an islands-in-sea
structure in which the binder resin forms the sea and the ester
compound and the low-melting material form the islands.
Thus, the present inventors consider that the effect brought by
both the good releasability and the good anchoring to recording
mediums enables achievement of a very good low-temperature fixing
performance.
The ester compound as in the present invention also has a higher
crystallinity and higher sharp-melt properties than any other
crystalline polymers, and hence is highly adaptable even to
printers or copying machines having high process speeds and
favorably usable also for on-demand fixing assemblies.
For such reasons, it is important that the toner of the present
invention contains the low-melting material and the specific ester
compound of dipentaerythritol and that, where the melting point of
the ester compound is represented by Tm.sub.(A) (.degree. C.) and
the melting point of the low-melting material is represented by
Tm.sub.(B) (.degree. C.), the toner satisfies the relationship of
Tm.sub.(B).ltoreq.Tm.sub.(A)+5.
If on the other hand the ester compound in the present invention is
a monoester or an ester compound having few functional groups, of
glycerol or erythrithol, or makes use of a carboxylic acid having
17 or less carbon atoms, such a compound tends to come to soak into
the resin to make it difficult to obtain the above effect,
resulting in an inferior fixing performance.
In addition, any use of a high-molecular material such as
tripentaerythrithol or a dehydration condensation product of
glycerol makes the ester compound tend to take various crystalline
states and hence have poor sharp-melt properties, resulting in a
lowering of fixing performance.
Further, any compound of dipentaerythritol with a carboxylic acid
having 26 or more carbon atoms may have too high a melting point to
achieve a good fixing performance with ease. Still further, such a
compound may inevitably come poorly dispersible in toner particles
to cause, e.g., fog seriously.
Then, if the low-melting material has a melting point higher by
more than 5.degree. C. than the melting point of the ester
compound, the push-out effect attributable to the ester compound
may be obtained with difficulty to make any good fixing performance
not achievable. The low-melting material may much preferably have a
melting point not higher than the melting point of the ester
compound (Tm.sub.(B).ltoreq.Tm.sub.(A)).
The ester compound used in the present invention may also
preferably have a solubility S(A) in a styrene-acrylic resin, of
2.5% or less, and much preferably 2.0% or less.
That the ester compound used in the present invention has a
solubility S(A) in a styrene-acrylic resin, of 2.5% or less is
preferable because the ester compound may soak into the resin with
greater difficulty to make the toner more improved in fixing
performance.
The solubility S(A) in a styrene-acrylic resin, of the ester
compound used in the present invention may be controlled by
controlling the number of carbon atoms of the carboxylic acid to be
used and the number of ester linkages.
The ester compound used in the present invention may have a
solubility in a styrene monomer at 40.degree. C., of less than 5.0%
by mass. This is much preferable because the above effect is
remarkably obtained. Where the toner is produced by suspension
polymerization, which is favorable in producing the present toner,
the ester compound may readily come deposited during the
polymerization where it has the solubility in that monomer, of less
than 5.0% by mass, and this makes cores readily formable in toner
particles, as so considered. In the present invention, the ester
compound has the function as stated above, and can be more
effective when firm cores stand formed in the toner particles, and
good fixing performance can be achieved, as so considered. Thus, it
is preferable for the ester compound to have the solubility in a
styrene monomer at 40.degree. C., of less than 5.0% by mass.
As the low-melting material used in the present invention, any
known wax may be used as long as it is one satisfying the
requirements prescribed herein. In particular, it is preferable
that the low-melting material has a solubility S(B) in a
styrene-acrylic resin, of from 5.5% or more to 20.0% or less and
that S(A)<S(B).
As to the reason therefor, the low-melting material as described
above can bring out good fixing performance by being pushed out by
the ester compound. However, where the low-melting material has the
solubility S(B) in a styrene-acrylic resin, of 5.5% or more, it
immediately plasticizes the binder resin of the toner when pushed
out, to effect better fixing. That the low-melting material has the
solubility S(B) in a styrene-acrylic resin, of 20.0% or less is
also preferable because the toner is improved in storage
stability.
That S(A)<S(B) is also preferable because the push-out effect
the ester compound has is more remarkably brought out and hence the
releasability is improved at the time of fixing.
The ester compound used in the present invention may preferably be
added in an amount of from 3.0 parts by mass or more to 20.0 parts
by mass or less, based on 100 parts by mass of the binder resin of
the toner.
The ester compound may be added in the amount within the above
range, where the ester compound can keep a good dispersibility to
bring a more improvement in developing performance. Further, this
is very preferable because the effect of pushing out the
low-melting material and the effect of promoting deformation of
toner particles in virtue of the liquid-at-core structure can be
sufficient.
The low-melting material used in the present invention may be in a
content from 1.2 times or more to 3.0 times or less the content of
the ester compound by mass. This is preferable because the toner
can achieve a good fixing performance and also can be improved in
developing performance and any fog can be kept from occurring.
The ester compound used in the present invention may preferably
have a melting point of from 70.degree. C. or more to 90.degree. C.
or less. Where the ester compound has its melting point within the
above rage, the toner can have a superior low-temperature fixing
performance and also can maintain a good image density even in
long-term service.
In order to develop minuter latent image dots for achieving much
higher image quality, the toner of the present invention may
preferably have a weight-average particle diameter (D4) of from 3
.mu.m or more to 12 .mu.m or less, and much preferably from 4 .mu.m
or more to 9 .mu.m or less.
The toner of the present invention may preferably have an average
circularity of 0.950 or more. Inasmuch as the toner has an average
circularity of from 0.950 or more, the toner has a spherical or
closely spherical particle shape and has a good fluidity, and can
readily have uniform triboelectric chargeability. This can make
ghost and electrostatic offset much less occur. The toner may also
have a modal circularity of 0.98 or more in its circularity
distribution. This is much preferable because the above operation
is more remarkable.
The toner of the present invention may preferably have a peak top
of the main peak in the region of molecular weight of from 10,000
or more to 40,000 or less, and much preferably have the peak top of
the main peak in the region of from 12,000 to 30,000, in its
molecular weight distribution measured by gel permeation
chromatography (GPC) of THF-soluble matter of the toner. That the
toner has the peak top in the region of molecular weight of from
10,000 or more to 40,000 or less is preferable because the toner is
improved in low-temperature fixing performance and also improved in
storage stability.
In the toner of the present invention, it is preferable that its
binder resin component has tetrahydrofuran(THF)-insoluble matter,
and that the THF-insoluble matter is in a content of from 5.0% by
mass or more to 65.0% by mass or less, based on the binder resin
component. The presence of such THF-insoluble matter in the toner
enhances the strength of toner and makes the toner not easily
deteriorate during long-term service, so that highly colorful
images can be obtained even during long-term service.
The toner melts by heat received from a fixing assembly at the time
of fixing, where, inasmuch as it has the THF-insoluble matter in a
content of from 5.0% by mass or more to 65.0% by mass or less, it
can have an appropriate elasticity even at the time of melting.
Hence, this is preferable because the toner can not easily cause
any high-temperature offset and can enjoy a broad fixing range.
The THF-insoluble matter of the binder resin component of the toner
may be measured in the following way. The toner is precisely
weighed in an amount of 1 g, which is then put in a cylindrical
filter paper and is subjected to Soxhlet extraction for 20 hours
using 200 ml of THF. Thereafter, the cylindrical filter paper is
taken out, and then vacuum-dried at 40.degree. C. for 20 hours to
measure the weight of residues. The THF-insoluble matter is
calculated according to the following expression. Here, the binder
resin component of the toner is the component obtained by removing
from the toner a charge control agent, release agent components
(the low-melting material and the low-melting material), external
additives, a pigment and a magnetic powder. In the measurement of
the THF-insoluble matter, whether or not these contents are soluble
or insoluble in THF is taken into account, and the THF-insoluble
matter on the basis of the binder resin component is calculated.
THF-insoluble matter (% by mass)={(W2-W3)/(W1-W3-W4)}.times.100
wherein W1 is the mass of toner; W2 is the mass of residues; W3 is
the mass of components insoluble in THF, other than the binder
resin component; and W4 is the mass of components soluble in THF,
other than the binder resin component.
The THF-insoluble matter of the binder resin component of the toner
may be controlled by combination of the types and amounts of a
polymerization initiator and a cross-linking agent which are to be
used. It may also be controlled by using a chain transfer agent and
the like.
The ester compound used in the present invention is a
hexafunctional ester having as an alcohol component the
dipentaerythritol and as an acid component the carboxylic acid
having 18 or more to 25 or less carbon atoms.
The carboxylic acid having 18 or more to 25 or less carbon atoms
may specifically include stearic acid, oleic acid, vaccenic acid,
linolic acid, eleostearic acid, tuberculostearic acid, arachidic
acid, arachidonic acid, behenic acid, lignoceric acid and nervonic
acid. In particular, saturated fatty acids are preferred.
The ester compound used in the present invention may preferably
have a hydroxyl value of 10 mgKOH/g or less and may preferably have
an acid value of 10 mgKOH/g or less. Having a hydroxyl value of 10
mgKOH/g or less and an acid value of 10 mgKOH/g or less means that
any unreacted acid component or unreacted alcohol component or any
ester compound that is not the hexafunctional ester is little
present. In this case, the ester compound can not easily come to
migrate toward toner particles surfaces during long-term storage of
the toner, and hence the toner can not easily become low in charge
quantity, and any density decrease or serious fog can be kept from
occurring.
The wax usable as the low-melting material used in the present
invention may include, e.g., petroleum waxes and derivatives
thereof such as paraffin wax, microcrystalline wax and petrolatum;
montan wax and derivatives thereof; hydrocarbon waxes obtained by
Fischer-Tropsch synthesis, and derivatives thereof; polyolefin
waxes typified by polyethylene wax, and derivatives thereof; and
naturally occurring waxes such as carnauba wax and candelilla wax,
and derivatives thereof. Here, the derivatives include oxides,
block copolymers with vinyl monomers, and graft modified products.
Also usable are higher aliphatic alcohols, fatty acids such as
stearic acid and palmitic acid, or compounds thereof, acid amide
waxes, ester waxes, ketones, hardened caster oil and derivatives
thereof, vegetable waxes, and animal waxes. Where a styrene
copolymer is used as the binder resin, paraffin wax and
Fischer-Tropsch wax are preferred, which may readily soak into the
resin at the time of melting. These waxes are those composed of
hydrocarbons having low molecular weight and having few branched
chains. In virtue of such structure, they have a high affinity for
the binder resin, as so presumed.
The binder resin used in the present invention may include
homopolymers of styrene or derivatives thereof, such as polystyrene
and polyvinyltoluene; styrene copolymers such as a
styrene-propylene copolymer, a styrene-vinyltoluene copolymer, a
styrene-vinylnaphthalene copolymer, a styrene-methyl acrylate
copolymer, a styrene-ethyl acrylate copolymer, a styrene-butyl
acrylate copolymer, a styrene-octyl acrylate copolymer, a
styrene-dimethylaminoethyl acrylate copolymer, a styrene-methyl
methacrylate copolymer, a styrene-ethyl methacrylate copolymer, a
styrene-butyl methacrylate copolymer, a styrene-dimethylaminoethyl
methacrylate copolymer, a styrene-methyl vinyl ether copolymer, a
styrene-ethyl vinyl ether copolymer, a styrene-methyl vinyl ketone
copolymer, a styrene-butadiene copolymer, a styrene-isoprene
copolymer, a styrene-maleic acid copolymer and a styrene-maleate
copolymer; and polymethyl methacrylate, polybutyl methacrylate,
polyvinyl acetate, polyethylene, polypropylene, polyvinyl butyral,
silicone resins, polyester resins, polyamide resins, epoxy resins
and polyacrylic acid resins. Any of these may be used alone or in
combination of two or more types. Of these resins, taking account
of the property that the ester compound used in the present
invention soaks into the resin together with the low-melting
material at the time of melting, styrene copolymers are
particularly preferred.
The toner of the present invention may optionally be mixed with a
charge control agent in order to improve charging performance. As
the charge control agent, any known charge control agent may be
used. In particular, charge control agents which can give speedy
charging and also can maintain a constant charge quantity stably
are preferred. Further, where the toner particles are produced by
polymerization as described later, it is particularly preferable to
use charge control agents having a low polymerization inhibitory
action and being substantially free of any solubilizate to the
aqueous dispersion medium. Among such charge control agents, as
specific compounds, they may include, as negative charge control
agents, metal compounds of aromatic carboxylic acids such as
salicylic acid, alkylsalicylic acids, dialkylsalicylic acids,
naphthoic acid and dicarboxylic acids; metal salts or metal
complexes of azo dyes or azo pigments; polymeric compounds having a
sulfonic acid or carboxylic acid group in the side chain; and boron
compounds, urea compounds, silicon compounds, and carixarene. As
positive charge control agents, they may include quaternary
ammonium salts, polymers having such a quaternary ammonium salt in
the side chain, guanidine compounds, Nigrosine compounds and
imidazole compounds.
As methods for making toner particles contain the charge control
agent, commonly available are a method of internally adding it to
the toner particles, and, in the case when the toner is produced by
suspension polymerization, a method in which the charge control
agent is added to a polymerizable monomer composition before its
granulation. A polymerizable monomer in which the charge control
agent has been dissolved or suspended may be added in the midst of
forming oil droplets in water to effect polymerization, or after
the polymerization, to carry out seed polymerization so as to cover
toner particle surfaces uniformly. Further, where an organometallic
compound is used as the charge control agent, such a compound may
be added to the toner particles and these may be mixed and agitated
under application of a shear to incorporate it into toner
particles.
The quantity of this charge control agent used depends on the type
of the binder resin, the presence of any other additives, and the
manner by which the toner is produced, inclusive of the manner of
dispersion, and can not absolutely be specified. When added
internally, however, the charge control agent may preferably be
used in an amount ranging from 0.1 part by mass or more to 10.0
parts by mass or less, and much preferably from 0.1 part by mass or
more to 5.0 parts by mass or less, based on 100 parts by mass of
the binder resin. When added externally, it may preferably be added
in an amount of from 0.005 part by mass or more to 1.000 part by
mass or less, and much preferably from 0.01 part by mass or more to
0.30 part by mass or less, based on 100 parts by mass of the toner
particles.
The toner of the present invention contains a colorant adapted to
the intended tint. The colorant used in the toner of the present
invention may include known organic pigments or dyes, carbon black
and magnetic powders, any of which may be used.
Stated specifically, as cyan colorants, usable are copper
phthalocyanine compounds and derivatives thereof, anthraquinone
compounds, basic dye lake compounds and so forth. Stated
specifically, they may include C.I. Pigment Blue 1, C.I. Pigment
Blue 7, C.I. Pigment Blue 15, C.I. Pigment Blue 15:1, C.I. Pigment
Blue 15:2, C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:4, C.I.
Pigment Blue 60, C.I. Pigment Blue 62 and C.I. Pigment Blue 66.
As magenta colorants, usable are condensation azo compounds,
diketopyrrolopyrrole compounds, anthraquinone compounds,
quinacridone compounds, basic-dye lake compounds, naphthol
compounds, benzimidazolone compounds, thioindigo compounds and
perylene compounds. Stated specifically, they may include C.I.
Pigment Red 2, C.I. Pigment Red 3, C.I. Pigment Red 5, C.I. Pigment
Red 6, C.I. Pigment Red 7, C.I. Pigment Red 19, C.I. Pigment Red
23, C.I. Pigment Red 48:2, C.I. Pigment Red 48:3, C.I. Pigment Red
48:4, C.I. Pigment Red 57:1, C.I. Pigment Red 81:1, C.I. Pigment
Red 122, C.I. Pigment Red 144, C.I. Pigment Red 146, C.I. Pigment
Red 166, C.I. Pigment Red 169, C.I. Pigment Red 177, C.I. Pigment
Red 184, C.I. Pigment Red 185, C.I. Pigment Red 202, C.I. Pigment
Red 206, C.I. Pigment Red 220, C.I. Pigment Red 221 and C.I.
Pigment Red 254.
As yellow colorants, usable are compounds typified by condensation
azo compounds, isoindolinone compounds, anthraquinone compounds,
azo metal complexes, methine compounds and allylamide compounds.
Stated specifically, they may include C.I. Pigment Yellow 12, C.I.
Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 15,
C.I. Pigment Yellow 17, C.I. Pigment Yellow 62, C.I. Pigment Yellow
74, C.I. Pigment Yellow 83, C.I. Pigment Yellow 93, C.I. Pigment
Yellow 94, C.I. Pigment Yellow 95, C.I. Pigment Yellow 97, C.I.
Pigment Yellow 109, C.I. Pigment Yellow 110, C.I. Pigment Yellow
111, C.I. Pigment Yellow 120, C.I. Pigment Yellow 127, C.I. Pigment
Yellow 128, C.I. Pigment Yellow 129, C.I. Pigment Yellow 147, C.I.
Pigment Yellow 151, C.I. Pigment Yellow 154, C.I. Pigment Yellow
168, C.I. Pigment Yellow 174, C.I. Pigment Yellow 175, C.I. Pigment
Yellow 176, C.I. Pigment Yellow 180, C.I. Pigment Yellow 181, C.I.
Pigment Yellow 191 and C.I. Pigment Yellow 194.
Any of these colorants may be used alone, in the form of a mixture,
or further in the state of a solid solution. The colorant used in
the toner of the present invention is selected taking account of
hue angle, chroma, brightness, light-fastness, transparency on OHP
films and dispersibility in toner particles. The colorant may
preferably be added in an amount of from 1 part by mass or more to
20 parts by mass or less, based on 100 parts by mass of the binder
resin.
As black colorants, carbon black, a magnetic powder and a colorant
toned in black by the use of yellow, magenta and cyan colorants
shown above may be used. In the case when the carbon black is used
as a black colorant, it may preferably be used in its addition in
an amount of from 1 part by mass or more to 20 parts by mass or
less, based on 100 parts by mass of the binder resin. Also, where
the toner of the present invention is used as a magnetic toner, the
magnetic powder may preferably be added in an amount of from 20
parts by mass or more to 150 parts by mass or less, based on 100
parts by mass of the binder resin.
In the case when the magnetic powder is used as the colorant, other
colorant may also be used in combination. Such a colorant usable in
combination may include magnetic or non-magnetic inorganic
compounds besides the above known dyes and pigments. Stated
specifically, it may include ferromagnetic metal particles of
cobalt, nickel or the like, or particles of alloys of any of these
metals to which chromium, manganese, copper, zinc, aluminum, a rare
earth element or the like has been added; as well as particles of
hematite or the like, titanium black, nigrosine dyes or pigments,
carbon black, and phthalocyanine. These may also be used after
their particle surface hydrophobic treatment.
The content of the magnetic powder in the toner may be measured
with a thermal analyzer TGA7, manufactured by Perkin-Elmer
Corporation. A measuring method is as follows: The toner is heated
at a heating rate of 25.degree. C./minute from normal temperature
to 900.degree. C. in an atmosphere of nitrogen. The mass (%) of
weight loss in the course of from 100.degree. C. to 750.degree. C.
is regarded as the binder resin weight, and the residual mass is
approximately regarded as the magnetic-powder weight.
In the case when in the present invention the toner is produced by
polymerization, attention must be paid to polymerization inhibitory
action or aqueous-phase transfer properties inherent in the
colorant. Accordingly, it is better for the colorant to be
beforehand subjected to surface modification, e.g., hydrophobic
treatment with a material free from polymerization inhibition. In
particular, most dyes and carbon black have the polymerization
inhibitory action and hence care must be taken when used. With
regard to the carbon black, it may be treated with a material
capable of reacting with surface functional groups of the carbon
black, as exemplified by a polyorganosiloxane.
In the case when the magnetic powder is used in the toner of the
present invention, the magnetic powder is what is chiefly composed
of a magnetic iron oxide such as triiron tetraoxide or .gamma.-iron
oxide, and may also contain any of elements such as phosphorus,
cobalt, nickel, copper, magnesium, manganese, aluminum and silicon.
Any of these magnetic powders may preferably have a BET specific
surface area, as measured by the nitrogen gas adsorption method, of
from 2 m.sup.2/g or more to 30 m.sup.2/g or less, and much
preferably from 3 m.sup.2/g or more to 28 m.sup.2/g or less. As the
particle shape of the magnetic powder, it may be, e.g., polygonal,
octahedral, hexahedral, spherical, acicular or flaky. Polygonal,
octahedral, hexahedral or spherical ones are preferred as having
less anisotropy, which are preferable in order to improve image
density.
The magnetic powder may preferably have a volume average particle
diameter (Dv) of from 0.10 .mu.m or more to 0.40 .mu.m or less.
That the magnetic powder has a volume average particle diameter
(Dv) of from 0.10 .mu.m or more to 0.40 .mu.m or less is preferable
because the magnetic powder can have a good dispersibility and the
toner is improved in coloring power.
The volume-average particle diameter of the magnetic powder may be
measured with a transmission electron microscope. Stated
specifically, toner particles to be observed are well dispersed in
epoxy resin, followed by curing for 2 days in an environment of
temperature 40.degree. C. to obtain a cured product. The cured
product obtained is cut out in slices by means of a microtome to
prepare a sample, where the particle diameter of 100
magnetic-powder particles in the visual field is measure on a
photograph taken at 10,000 magnifications to 40,000 magnifications
using a transmission electron microscope (TEM). Then, the
volume-average particle diameter (Dv) is calculated on the basis of
circle-equivalent diameter equal to the particle projected area of
the magnetic powder. The particle diameter may also be measured
with an image analyzer.
The magnetic powder usable in the present invention may be produced
in the following way, for example. To an aqueous ferrous salt
solution, an alkali such as sodium hydroxide is added in an
equivalent weight, or more than equivalent weight, with respect to
the iron component to prepare an aqueous solution containing
ferrous hydroxide. Into the aqueous solution thus prepared, air is
blown while its pH is maintained at pH 7 or above, and the ferrous
hydroxide is made to undergo oxidation reaction while the aqueous
solution is heated at 70.degree. C. or more to firstly form seed
crystals serving as cores of magnetic ion oxide particles.
Next, to a slurry-like liquid containing the seed crystals, an
aqueous solution containing ferrous sulfate in about one equivalent
weight on the basis of the quantity of the alkali previously added
is added. The reaction of the ferrous hydroxide is continued while
the pH of the liquid is maintained at 5 or more to 10 or less and
air is blown, to cause magnetic iron oxide particles to grow about
the seed crystals as cores. At this stage, any desired pH, reaction
temperature and stirring conditions may be selected so that the
particle shape and magnetic properties of the magnetic powder can
be controlled. With progress of oxidation reaction, the pH of the
liquid comes to shift to acid side, but the pH of the liquid may
preferably be so adjusted as not to be made less than 5. The
magnetic material thus obtained may be filtered, followed by
washing and then drying all by conventional methods to obtain the
magnetic powder.
In the case when in the present invention the toner is produced by
polymerization, it is very preferable for the particle surfaces of
the magnetic powder to be subjected to hydrophobic treatment. Where
such hydrophobic treatment is carried out by a dry process, a
coupling agent is added to the magnetic powder obtained as a result
of washing, filtration and drying, to carry out hydrophobic
treatment. Where the hydrophobic treatment is carried out by a wet
process, those having been dried after the oxidation reaction has
been completed are again dispersed. As another method, the iron
oxide material obtained by the oxidation reaction having been
completed, followed by washing and filtration, may be again
dispersed in a different aqueous medium without being dried, where
a coupling agent may be added to carry out hydrophobic treatment.
Stated specifically, a silane coupling agent is added to the one
dispersed again, with its thorough stirring, and the temperature
may be raised after hydrolysis or the pH may be adjusted to the
alkaline side to carry out hydrophobic treatment. Of these, from
the viewpoint of carrying out uniform hydrophobic treatment, it is
preferable that what has been obtained by the oxidation reaction
having been completed, followed by filtration and washing, is
formed into a slurry as it is, without being dried, and then the
hydrophobic treatment is carried out.
To carry out the hydrophobic treatment of the magnetic powder by
the wet process, i.e., the magnetic powder is hydrophobic-treated
in an aqueous medium, the magnetic powder is first sufficiently
dispersed in the aqueous medium so as to become primary particles,
and then stirred with a stirring blade or the like so as not to
settle or agglomerate. Next, the coupling agent is introduced in
the resultant dispersion in any desired amount, and the hydrophobic
treatment is carried out while hydrolyzing the coupling agent. In
this case as well, it is much preferable to carry out the
hydrophobic treatment while carrying out dispersion sufficiently so
as not to cause agglomeration, with stirring and using an apparatus
such as a pin mill or a line mill.
Here, the aqueous medium is a medium composed chiefly of water.
Stated specifically, it may include water itself, water to which a
surface-active agent has been added in a small quantity, water to
which a pH adjuster has been added, and water to which an organic
solvent has been added. As the surface-active agent, a nonionic
surface-active agent such as polyvinyl alcohol is preferred. The pH
adjuster may include inorganic acids such as hydrochloric acid. The
organic solvent may include alcohols.
The coupling agent usable in the hydrophobic treatment of the
magnetic powder in the present invention may include, e.g., silane
coupling agents and titanium coupling agents. Preferably usable is
a silane coupling agent, which is one represented by the general
formula (A): R.sub.mSiY.sub.n (A)
wherein R represents an alkoxyl group; m represents an integer of 1
or more to 3 or less; Y represents a functional group such as an
alkyl group, a vinyl group, an epoxy group, an acrylic group or a
methacrylic group; and n represents an integer of 1 or more to 3 or
less, provided that m+n=4.
The silane coupling agent represented by the general formula (A)
may include, e.g., vinyltrimethoxysilane, vinyltriethoxysilane,
vinyltris(.beta.-methoxyethoxy)silane,
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane,
.gamma.-glycidoxypropylmethyldiethoxysilane,
.gamma.-aminopropyltriethoxysilane,
N-phenyl-.gamma.-aminopropyltrimethoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane,
methyltrimethoxysilane, dimethyldimethoxysilane,
phenyltrimethoxysilane, diphenyldimethoxysilane,
methyltriethoxysilane, dimethyldiethoxysilane,
phenyltriethoxysilane, diphenyldiethoxysilane,
n-butyltrimethoxysilane, isobutyltrimethoxysilane,
trimethylmethoxysilane, n-hexyltrimethoxysilane,
n-octyltrimethoxysilane, n-octyltriethoxysilane,
n-decyltrimethoxysilane, hydroxypropyltrimethoxysilane,
n-hexadecyltrimethoxysilane and n-octadecyltrimethoxysilane.
Of these, from the viewpoint of providing the magnetic powder with
a high hydrophobicity, an alkyltrialkoxysilane compound represented
by the following formula (B) may preferably be used.
C.sub.pH.sub.2q+1--Si--(OC.sub.pH2.sub.q+1).sub.3 (B)
wherein p represents an integer of 2 or more to 20 or less, and q
represents an integer of 1 or more to 3 or less.
In the above formula, if p is smaller than 2, it is difficult to
provide the magnetic powder with a sufficient hydrophobicity. If p
is larger than 20, though hydrophobicity can be sufficient, the
magnetic powder particles may greatly coalesce one another,
undesirably. Further, if q is larger than 3, the silane compound
may have a low reactivity to make it hard for the magnetic powder
to be made sufficiently hydrophobic. Accordingly, it is preferable
to use an alkyltrialkoxysilane compound in which the p in the
formula represents an integer of 2 or more to 20 or less (much
preferably an integer of 3 or more to 15 or less) and the q
represents an integer of 1 or more to 3 or less (much preferably an
integer of 1 or 2).
In the case when the above silane compound is used, the treatment
may be carried out using it alone, or using a plurality of types in
combination. In using a plurality of types in combination, the
treatment may be carried out using the respective coupling agents
separately, or the treatment may be carried out using them
simultaneously.
The silane compound used may preferably be in a total treatment
quantity of from 0.9 part by mass or more to 3.0 parts by mass or
less, based on 100 parts by mass of the magnetic powder, and it is
important to control the amount of the treating agent in accordance
with the surface area of the magnetic powder, the reactivity of the
silane compound, and so forth.
The toner of the present invention may preferably have a glass
transition temperature (Tg) of from 40.degree. C. or more to
70.degree. C. or less. That it has a glass transition temperature
of from 40.degree. C. or more to 70.degree. C. or less is
preferable because the toner can achieve both fixing performance
and storage stability.
The toner of the present invention may preferably have a core-shell
structure in order to improve its storage stability and more
improve its developing performance. This is because having shell
layers makes the toner particles uniform in surface properties,
improved in fluidity and also uniform in chargeability.
In addition, since the shell uniformly covers the surface layer,
the bleeding of the low-melting material hardly occurs even during
long-term storage of toner, so that the toner is improved in the
storage stability.
To that end, it is preferable for the shell layers to use an
amorphous resin for shells, which may preferably have an acid value
of 5.0 mgKOH/g or more to 20.0 mgKOH/g or less from the viewpoint
of the stability of charging.
As a specific means for forming such shells, fine particles for
shells may be buried in core particles. Also, where the toner is
produced in an aqueous medium, which is a production method
favorable for the present invention, ultrafine particles for shells
may be made to adhere to core particles, followed by drying to form
shell layers. Still also, when produced by solution polymerization
or suspension polymerization, the acid value and hydrophilicity of
a resin for shells may be utilized to make such a high-molecular
weight material localized at the interface between it and water,
i.e., at toner particles surfaces and in the vicinity thereof to
form shell layers. Further, a monomer may be swelled on core
particle surfaces and polymerized by what is called seed
polymerization, to form shell layers.
The resin for shells may include, e.g., homopolymers of styrene or
derivatives thereof, such as polystyrene and polyvinyltoluene;
styrene copolymers such as a styrene-propylene copolymer, a
styrene-vinyltoluene copolymer, a styrene-vinylnaphthalene
copolymer, a styrene-methyl acrylate copolymer, a styrene-ethyl
acrylate copolymer, a styrene-butyl acrylate copolymer, a
styrene-octyl acrylate copolymer, a styrene-dimethylaminoethyl
acrylate copolymer, a styrene-methyl methacrylate copolymer, a
styrene-ethyl methacrylate copolymer, a styrene-butyl methacrylate
copolymer, a styrene-dimethylaminoethyl methacrylate copolymer, a
styrene-methyl vinyl ether copolymer, a styrene-ethyl vinyl ether
copolymer, a styrene-methyl vinyl ketone copolymer, a
styrene-butadiene copolymer, a styrene-isoprene copolymer, a
styrene-maleic acid copolymer and a styrene-maleate copolymer; and
polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate,
polyethylene, polypropylene, polyvinyl butyral, silicone resins,
polyester resins, a styrene-polyester copolymer, a
polyacrylate-polyester copolymer, a polymethacrylate-polyester
copolymer, polyamide resins, epoxy resins, polyacrylic acid resins,
terpene resins and phenol resins. Any of these may be used alone or
in combination of two or more types. A functional group such as an
amino group, a carboxyl group, a hydroxyl group, a sulfonic acid
group, a glycidyl group or a nitrile group may also be introduced
into any of these polymers.
Any of these resins may preferably be added in an amount of from 1
part by mass or more to 30 parts by mass or less, based on 100
parts by mass of the polymerizable monomer.
Of these resins, polyester resin is preferred because it can
greatly bring out the above effect. The polyester resin used in the
present invention may be either or both of a saturated polyester
resin and an unsaturated polyester resin, which may be used under
appropriate selection.
The resin that forms shells may have a number average molecular
weight of from 2,500 or more to 10,000 or less, which may
preferably be used. This is preferable because one having a number
average molecular weight of 2,500 or more brings improvements in
anti-blocking properties and running performance and one having a
number average molecular weight of 10,000 or less does not inhibit
the low-temperature fixing performance. The number average
molecular weight may be measured by GPC.
The toner of the present invention may be produced by any known
process. First, where it is produced by a pulverization process,
for example, components necessary as the toner, such as the binder
resin, the colorant, the ester compound and the low-melting
material, and other additives, are thoroughly mixed by means of a
mixer such as Henschel mixer or a ball mill. Thereafter, the
mixture obtained is melt-kneaded by means of a heat kneading
machine such as a heat roll, a kneader or an extruder to make toner
materials dispersed or dissolved, followed by cooling to solidify,
then pulverization, thereafter classification, and optionally
surface treatment to obtain toner particles. Either of the
classification and the surface treatment may be first in order. In
the step of classification, a multi-division classifier may
preferably be used in view of production efficiency.
The pulverization step may be carried out by using a known
pulverizer such as a mechanical impact type or a jet type. In order
to obtain the toner having the specific circularity preferable in
the present invention, it is preferable to further apply heat to
effect pulverization or to carry out treatment of adding mechanical
impact auxiliarily. Also usable are a hot-water bath method in
which toner particles finely pulverized (and optionally classified)
are dispersed in hot water, a method in which the toner particles
are passed through hot-air streams, and so forth.
As means for applying mechanical impact force, available are, e.g.,
a method making use of a mechanical impact type pulverizer such as
Kryptron system, manufactured by Kawasaki Heavy Industries, Ltd.,
or Turbo mill, manufactured by Turbo Kogyo Co., Ltd. A method may
also be used in which toner particles are pressed against the inner
wall of a casing by centrifugal force by means of a high-speed
rotating blade to impart mechanical impact force to the toner
particles by the force such as compression force or frictional
force, as in apparatus such as a mechanofusion system manufactured
by Hosokawa Micron Corporation or a hybridization system
manufactured by Nara Machinery Co., Ltd.
The toner of the present invention may be produced by the
pulverization process as described above. However, the toner
particles obtained by such pulverization commonly have an amorphous
shape, and hence any mechanical and thermal or any special
treatment must be carried out in order to attain the physical
properties that the average circularity is 0.950 or more, which is
preferably used in the present invention. This may result in an
inferior productivity. Accordingly, the toner of the present
invention may preferably be obtained by producing toner particles
in an aqueous medium, as in dispersion polymerization, association
agglomeration, dissolution suspension or suspension polymerization.
In particular, suspension polymerization may readily satisfy
preferable physical properties required in the present invention,
and is very preferred.
The suspension polymerization is a process in which the
polymerizable monomer and the colorant (and further optionally a
polymerization initiator, a cross-linking agent, a charge control
agent and other additives) are uniformly dissolved or dispersed to
make up a polymerizable monomer composition, and thereafter this
polymerizable monomer composition is dispersed in a continuous
phase (e.g., an aqueous phase) containing a dispersion stabilizer,
by means of a suitable stirrer to carry out polymerization to
obtain a toner having the desired particle diameters. In the toner
obtained by this suspension polymerization (hereinafter also termed
"polymerization toner"), the individual toner particles stand
uniform in a substantially spherical shape, and hence the toner can
readily obtained which satisfies the requirement on physical
properties that the average circularity is 0.950 or more, which is
preferable in the present invention. Moreover, such a toner can
have a relatively uniform distribution of charge quantity, and
hence can be expected to be improved in image quality.
In producing the polymerization toner according to the present
invention, the polymerizable monomer making up the polymerizable
monomer composition may include the following.
The polymerizable monomer may include styrene; styrene monomers
such as o-methylstyrene, m-methylstyrene, p-methylstyrene,
p-methoxystyrene and p-ethylstyrene; acrylic esters such as methyl
acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate,
n-propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl
acrylate, stearyl acrylate, 2-chloroethyl acrylate and phenyl
acrylate; methacrylic esters such as methyl methacrylate, ethyl
methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl
methacrylate, n-octyl methacrylate, dodecyl methacrylate,
2-ethylhexyl methacrylate, stearyl methacrylate, phenyl
methacrylate, dimethylaminoethyl methacrylate and diethylaminoethyl
methacrylate; and other monomers such as acrylonitrile,
methacrylonitrile and acrylamides. Any of these monomers may be
used alone or in the form of a mixture. Of the foregoing monomers,
styrene or a styrene derivative may preferably be used alone or in
the form of a mixture with other monomer. This is preferable in
view of developing performance and running performance of the
toner.
As the polymerization initiator used in producing the toner of the
present invention by polymerization, preferred is one having a
half-life of from 0.5 hour or more to 30.0 hours or less. It may
also be used in its addition in an amount of from 0.5 part by mass
or more to 20 parts by mass or less, based on 100 parts by mass of
the polymerizable monomer, to carry out polymerization. This
enables the toner to be endowed with a desirable strength and
appropriate melt properties.
As a specific polymerization initiator, it may include azo type or
diazo type polymerization initiators such as
2,2'-azobis-(2,4-dimethylvaleronitrile),
2,2'-azobisisobutyronitrile,
1,1'-azobis-(cyclohexane-1-carbonitrile),
2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile and
azobisisobutyronitrile; and peroxide type polymerization initiators
such as benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl
peroxycarbonate, cumene hydroperoxide, 2,4-dichlorobenzoyl
peroxide, lauroyl peroxide, t-butyl peroxy-2-ethylhexanoate and
t-butyl peroxypivarate.
In producing the toner of the present invention by polymerization,
a cross-linking agent may be added, which may preferably be added
in an amount of from 0.001 part by mass or more to 15.000 parts by
mass or less, based on 100 parts by mass of the polymerizable
monomer.
Here, as the cross-linking agent, compounds chiefly having at least
two polymerizable double bonds may be used. It may include, e.g.,
aromatic divinyl compounds such as divinyl benzene and divinyl
naphthalene; carboxylic acid esters having two double bonds, such
as ethylene glycol diacrylate, ethylene glycol dimethacrylate and
1,3-butanediol dimethacrylate; divinyl compounds such as divinyl
aniline, divinyl ether, divinyl sulfide and divinyl sulfone; and
compounds having at least three vinyl groups; any of which may be
used alone or in the form of a mixture of two or more types.
In the method of producing the toner of the present invention by
polymerization, commonly a polymerizable monomer composition
prepared by adding the above toner-composing materials
appropriately and dissolving or dispersing them by means of a
dispersion machine such as a homogenizer, a ball mill or an
ultrasonic dispersion machine is suspended in an aqueous medium
containing a dispersion stabilizer. Here, a high-speed dispersion
machine such as a high-speed stirrer or an ultrasonic dispersion
machine may be used to make the toner particles have the desired
particle size at a stretch. This can more readily make the
resultant toner particles have a sharp particle size distribution.
As the time at which the polymerization initiator is added, it may
be added simultaneously when other additives are added to the
polymerizable monomer, or may be mixed immediately before they are
suspended in the aqueous medium. Also, immediately after
granulation, the polymerization initiator may be added before the
polymerization reaction is initiated.
After granulation, agitation may be carried out using a usual
agitator in such an extent that the state of particles is
maintained and also the particles can be prevented from floating
and settling.
When the toner of the present invention is produced by
polymerization, any of known surface-active agents or organic or
inorganic dispersants may be used as a dispersion stabilizer. In
particular, the inorganic dispersants may preferably be used
because they may hardly cause any harmful ultrafine powder and they
attain dispersion stability on account of their steric hindrance.
As examples of such inorganic dispersants, they may include
phosphoric acid polyvalent metal salts such as tricalcium
phosphate, magnesium phosphate, aluminum phosphate, zinc phosphate
and hydroxyl apatite; carbonates such as calcium carbonate and
magnesium carbonate; inorganic salts such as calcium metasilicate,
calcium sulfate and barium sulfate; and inorganic compounds such as
calcium hydroxide, magnesium hydroxide and aluminum hydroxide.
Any of these inorganic dispersants may preferably be used in an
amount of from 0.2 part by mass or more to 20.0 parts by mass or
less, based on 100 parts by mass of the polymerizable monomer. The
dispersion stabilizer may also be used alone or in combination of
two or more types. It may further be used in combination with a
surface-active agent.
Such a surface-active agent may include, e.g., sodium
dodecylbenzene sulfate, sodium tetradecyl sulfate, sodium
pentadecyl sulfate, sodium octyl sulfate, sodium oleate, sodium
laurate, sodium stearate and potassium stearate.
In the step of polymerizing the polymerizable monomer, the
polymerization may be carried out at a polymerization temperature
set at 40.degree. C. or more, and commonly at a temperature of from
50.degree. C. or more to 90.degree. C. or less. Inasmuch as the
polymerization is carried out within this temperature range, the
low-melting material to be enclosed in interiors is deposited by
phase separation to come more perfectly enclosed in toner
particles.
The polymerization toner particles may be, after the polymerization
has been completed, subjected to filtration, washing and drying by
conventional methods to obtain the toner particles. The toner
particles thus obtained may optionally be mixed with an inorganic
fine powder describe later. A classification step may also be added
(before mixing with the inorganic fine powder) so as to remove
coarse powder and fine powder present mixedly with the toner
particles.
In the present invention, an inorganic fine powder having a
number-average primary particle diameter (D1) of from 4 nm or more
to 80 nm or less, and preferably from 6 nm or more to 40 nm or
less, may externally be added to the toner particles as a
fluidizing agent. This is also a preferred embodiment. The
inorganic fine powder is added in order to improve the fluidity of
the toner and make the charging of the toner particles uniform,
where the inorganic fine powder may be subjected to treatment such
as hydrophobic treatment so that the toner may further be endowed
with the function to regulate its charge quantity and improve its
environmental stability. This is also a preferred embodiment.
In the present invention, the number-average primary particle
diameter (D1) of the inorganic fine powder may be measured with a
scanning electron microscope, using a photograph of toner particles
which is taken under magnification.
As the inorganic fine powder used in the present invention, fine
silica powder, fine titanium oxide powder, fine alumina powder or
the like may be used. As the fine silica powder, usable are, e.g.,
what is called dry-process silica or fumed silica produced by vapor
phase oxidation of silicon halides and what is called wet-process
silica produced from water glass or the like, either of which may
be used. The dry-process silica is preferred, as having less
silanol groups on the particle surfaces and particle interiors of
the fine silica powder and leaving less production residues such as
Na.sub.2O and SO.sub.3.sup.2-.
The above inorganic fine powder may preferably be added in an
amount of from 0.1 part by mass or more to 3.0 parts by mass or
less, based on 100 parts by mass of the toner particles. The
content of the inorganic fine powder may quantitatively be
determined by fluorescent X-ray analysis and using a calibration
curve prepared from a standard sample.
In the present invention, the inorganic fine powder may be a powder
having been hydrophobic-treated. This is preferable because the
toner can be improved in environmental stability. Where the
inorganic fine powder added to the toner has moistened, the toner
particles may have a very low charge quantity and tend to have a
non-uniform charge quantity, tending to cause toner scatter. As a
treating agent used for such hydrophobic treatment of the inorganic
fine powder, usable are treating agents such as a silicone varnish,
a modified silicone varnish of various types, a silicone oil, a
modified silicone oil of various types, a silane compound, a silane
coupling agent, other organosilicon compound and an organotitanium
compound, any of which may be used alone or in combination of two
or more types.
Of such treating agents, those having been treated with silicone
oil are preferred. Those obtained by subjecting the inorganic fine
powder to hydrophobic treatment with a silane compound and,
simultaneously with or after the treatment, treatment with silicone
oil are much preferred. As a method for such treatment of the
inorganic fine powder, for example, the inorganic fine powder may
be treated, as first-stage reaction, with the silane compound to
effect silylation reaction to cause silanol groups to disappear by
chemical coupling, and thereafter, as second-stage reaction, with
the silicone oil to form hydrophobic thin films on particle
surfaces.
In order to, e.g., improve cleaning performance, inorganic or
organic closely spherical fine particles having a number average
particle diameter (D1) of 30 nm or more, and much preferably of 50
nm or more, may be added to the toner of the present invention.
This is also one of preferred embodiments. For example, spherical
silica particles, spherical polymethyl silsesquioxane particles or
spherical resin particles may preferably be used.
How to measure various physical properties concerning the toner of
the present invention is described below.
(1) Melting Points of Ester Compound and Low-Melting Material
The melting points of the ester compound and low-melting material
are each found as a peak top of endothermic peaks when measured by
DSC. The peak top of endothermic peaks is measured according to
ASTM D34117-99. For the measurement, DSC-7, manufactured by
Perkin-Elmer Corporation, DSC2920, manufactured by TA Instruments
Japan Ltd., or Q1000, manufactured by TA Instruments Japan Ltd.,
may be used, for example. The temperature at the detecting portion
of the measuring instrument is corrected on the basis of melting
points of indium and zinc, and the amount of heat is corrected on
the basis of heat of fusion of indium. The sample for measurement
is put in a pan made of aluminum and an empty pan is set as a
control.
(2) Weight Average Particle Diameter (D4) of Toner
The weight average particle diameter (D4) the toner is measured in
the following way. A precision particle size distribution measuring
instrument "Coulter Counter Multisizer 3" (registered trademark;
manufactured by Beckman Coulter, Inc.) is used as a measuring
instrument, which has an aperture tube of 100 .mu.m in size and
employing the aperture impedance method. To set the conditions for
measurement and analyze the data of measurement, a software
"Beckman Coulter Multisizer 3 Version 3.51" (produced by Beckman
Coulter, Inc.) is used, which is attached to Multisizer 3 for its
exclusive use. The measurement is made through 25,000 channels as
effective measuring channels in number.
As an aqueous electrolytic solution used for the measurement, a
solution may be used which is prepared by dissolving guaranteed
sodium chloride in ion-exchanged water in a concentration of about
1% by mass, e.g., "ISOTON II" (available from Beckman Coulter,
Inc.).
Here, before the measurement and analysis are made, the software
for exclusive use is set in the following way.
On a "Change of Standard Measuring Method (SOM)" screen of the
software for exclusive use, the total number of counts of a control
mode is set to 50,000 particles. The number of time of measurement
is set to one time and, as Kd value, the value is set which has
been obtained using "Standard Particles, 10.0 .mu.m" (available
from Beckman Coulter, Inc.). Threshold value and noise level are
automatically set by pressing "Threshold Value/Noise Level
Measuring Button". Then, current is set to 1,600 .mu.A, gain to 2,
and electrolytic solution to ISOTON II, where "Flash for Aperture
Tube after Measurement" is checked.
On a "Setting of Conversion from Pulse to Particle Diameter" screen
of the software for exclusive use, the bin distance is set to
logarithmic particle diameter, the particle diameter bin to 256
particle diameter bins, and the particle diameter range to from 2
.mu.m to 60 .mu.m.
A specific way of measurement is as follows:
(i) About 200 ml of the aqueous electrolytic solution is put into a
250 ml round-bottomed beaker made of glass for exclusive use in
Multisizer 3, and this is set on a sample stand, where stirring
with a stirrer rod is carried out at 24 revolutions/second in the
anticlockwise direction. Then, "Flash of Aperture" function of the
analysis software is operated to beforehand remove any dirt and air
bubbles in the aperture tube. (ii) About 30 ml of the aqueous
electrolytic solution is put into a 100 ml flat-bottomed beaker
made of glass. To this water, about 0.3 ml of a dilute solution is
added as a dispersant, which has been prepared by diluting
"CONTAMINON N" (an aqueous 10% by mass solution of a pH 7 neutral
detergent for washing precision measuring instruments which is
composed of a nonionic surface-active agent, an anionic
surface-active agent and an organic builder and is available from
Wako Pure Chemical Industries, Ltd.) with ion-exchanged water to
about 3-fold by mass. (iii) An ultrasonic dispersion machine of 120
W in electric output "Ultrasonic Dispersion system TETORA 150"
(manufactured by Nikkaki Bios Co.) is readied, having two
oscillators of 50 kHz in oscillation frequency which are built
therein in the state their phases are shifted by 180 degrees. Into
a water tank of the ultrasonic dispersion machine, about 3.3 liters
of ion-exchanged water is put, and about 2 ml of CONTAMINON N is
added to this water tank. (iv) The beaker of the above (ii) is set
to a beaker fixing hole of the ultrasonic dispersion machine, and
the ultrasonic dispersion machine is set working. Then, the height
position of the beaker is so adjusted that the state of resonance
of the aqueous electrolytic solution surface in the beaker may
become highest. (v) In the state the aqueous electrolytic solution
in the beaker of the above (iv) is irradiated with ultrasonic
waves, about 10 mg of the toner is little by little added to the
aqueous electrolytic solution and is dispersed therein. Then, such
ultrasonic dispersion treatment is further continued for 60
seconds. In carrying out the ultrasonic dispersion treatment, the
water temperature of the water tank is appropriately so controlled
as to be 10.degree. C. or more to 40.degree. C. or less. (vi) To
the round-bottomed beaker of the above (i), placed inside the
sample stand, the aqueous electrolytic solution in which the toner
has been dispersed in the above (v) is dropwise added by using a
pipette, and the measuring concentration is so adjusted as to be
about 5%. Then the measurement is made until the measuring
particles come to 50,000 particles in number. (vii) The data of
measurement are analyzed by using the above software attached to
the measuring instrument for its exclusive use, to calculate the
weight average particle diameter (D4). Here, "Average Diameter" on
an "Analysis/Volume Statistic Value (Arithmetic Mean)" screen when
set to graph/% by volume in the software for exclusive use is the
weight average particle diameter (D4).
Measurement of Average Circularity of Toner
The average circularity of the toner is measured with a flow type
particle analyzer "FPIA-2100" (manufactured by Sysmex Corporation).
Details are as follows.
First, circularity is calculated according to the following
expression. Circularity=(circumferential length of a circle with
the same area as particle projected area)/(circumferential length
of particle projected image).
Herein, the "particle projected area" is the area of a binary-coded
toner particle image, and the "circumferential length of particle
projected image" is the length of a contour line formed by
connecting edge points of the toner particle image. In the
measurement, used is the circumferential length of a particle image
in image processing at an image processing resolution of
512.times.512 (a pixel of 0.3 .mu.m.times.0.3 .mu.m).
The circularity referred to in the present invention is an index
showing the degree of surface unevenness of toner particles. It is
indicated as 1.00 when the toner particles are perfectly spherical.
The more complicate the surface shape is, the smaller the value of
circularity is.
Average circularity C which means an average value of circularity
frequency distribution is calculated from the following expression
where the circularity at a partition point i of particle size
distribution is represented by ci, and the number of particles
measured by m.
.times..times..times..times..times. ##EQU00001##
A specific way of measurement is as follows: First, about 10 ml of
ion-exchanged water, from which impurity solid matter and the like
have beforehand been removed, is put into a container made of
glass. To this water, about 0.1 ml of a dilute solution is added as
a dispersant, which has been prepared by diluting "CONTAMINON N"
(an aqueous 10% by mass solution of a pH 7 neutral detergent for
washing precision measuring instruments which is composed of a
nonionic surface-active agent, an anionic surface-active agent and
an organic builder and is available from Wako Pure Chemical
Industries, Ltd.) with ion-exchanged water to about 3-fold by mass.
Further, about 0.02 g of a measuring sample is added, followed by
dispersion treatment for 2 minutes by means of an ultrasonic
dispersion machine to prepare a liquid dispersion for measurement.
As the ultrasonic dispersion machine, an ultrasonic dispersion
machine of 120 W in electric output "Ultrasonic Dispersion system
TETORA 150 Model" (manufactured by Nikkaki Bios Co.) is used,
having two oscillators of 50 kHz in oscillation frequency which are
built therein in the state their phases are shifted by 180 degrees.
Into an water tank of the ultrasonic dispersion machine, about 3.3
liters of ion-exchanged water is put, and about 2 ml of CONTAMINON
N is added to this water tank. In that case, the liquid dispersion
is appropriately cooled so that its temperature does not become
40.degree. C. or more. Also, in order to keep the circularity from
scattering, the environment in which the flow type particle
analyzer FPIA-2100 is installed is controlled to 23.degree.
C..+-.0.5.degree. C. so that the in-machine temperature of the
analyzer can be kept at 26.degree. C. to 27.degree. C. Still also,
autofocus control is performed using 2 .mu.m standard latex
particles (e.g., "RESEARCH AND TEST PARTICLES Latex Microsphere
Suspensions 5200A, available from Duke Scientific Corporation) at
intervals of constant time, and preferably at intervals of 2
hours.
In measuring the circularity of the toner particles, the above flow
type particle analyzer is used and PARTICLE SHEATH PSE-900A
(available from Sysmex Corporation) is used as a sheath solution.
The liquid dispersion having been controlled according to the above
procedure is introduced into the flow type particle analyzer, where
the concentration of the liquid dispersion is again so controlled
that the toner particle concentration at the time of measurement
may be about 5,000 particles/.mu.l. After the measurement, using
the data obtained, the average circularity of toner particles with
a circle-equivalent diameter of from 2.00 .mu.m or more to less
than 40.02 .mu.m is determined. Here, the circle-equivalent
diameter is the value calculated according to the following
expression. Circle-equivalent diameter=(particle projected
area/.pi.).sup.1/2.times.2.
(4) Measurement of Molecular Weight of THF-Soluble Matter of
Toner
Molecular weight distribution of THF-soluble matter of the toner is
measured by gel permeation chromatography (GPC) in the following
way.
First, the toner is dissolved in tetrahydrofuran (THF) at room
temperature over a period of 24 hours. Then, the solution obtained
is filtered with a solvent-resistant membrane filter "MAISHORIDISK"
(available from Tosoh Corporation) of 0.2 .mu.m in pore diameter to
make up a sample solution. Here, the sample solution is so
controlled that the component soluble in THF is in a concentration
of about 0.8% by mass. Using this sample solution, the measurement
is made under the following conditions.
Instrument: HLC8120 GPC (detector: RI) (manufactured by Tosoh
Corporation).
Columns: Combination of seven columns, Shodex KF-801, KF-802,
KF-803, KF-804, KF-805, KF-806 and KF-807 (available from Showa
Denko K.K.).
Eluent: Tetrahydrofuran (THF).
Flow rate: 1.0 ml/min.
Oven temperature: 40.0.degree. C.
Amount of sample injected: 0.10 ml.
To calculate the molecular weight of the sample, a molecular weight
calibration curve is used which is prepared using a standard
polystyrene resin (e.g., trade name "TSK Standard Polystyrene
F-850, F-450, F-288, F-128, F-80, F-40, F-20, F-10, F-4, F-2, F-1,
A-5000, A-2500, A-1000, A-500"; available from Tosoh
Corporation).
(5) Solubility of Ester Compound and Low-Melting Material in
Styrene-Acrylic Resin
The solubility of the ester compound and low-melting material in
styrene-acrylic resin is measured in the following way.
First, the styrene-acrylic resin is synthesized in the following
way.
In 720 parts by mass of ion-exchanged water, 450 parts by mass of
an aqueous 0.1 mol/liter Na.sub.3PO.sub.4 solution is introduced,
followed by heating to 60.degree. C. Thereafter, to the resultant
mixture, 67.7 parts by mass of an aqueous 1.0 mol/liter CaCl.sub.2
solution is little by little added to obtain an aqueous medium
containing a dispersion stabilizer.
TABLE-US-00001 Styrene 76.0 parts by mass n-Butyl acrylate 24.0
parts by mass
Materials formulated as above are uniformly mixed using an attritor
(manufactured by Mitsui Miike Engineering Corporation). The monomer
mixture thus obtained is heated to 60.degree. C., and thereafter
4.5 parts by mass of a polymerization initiator
2,2'-azobis(2,4-dimethylvaleronitrile) is dissolved therein.
The polymerizable monomer composition thus prepared is introduced
into the above aqueous medium, followed by stirring for 10 minutes
at 60.degree. C. in an atmosphere of N.sub.2, using a TK-type
homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) at 12,000
rpm to carry out granulation. Thereafter, the granulated product
obtained is stirred with a paddle stirring blade during which the
reaction was carried out at 70.degree. C. for 5 hours. After the
reaction has been completed, the resultant suspension is cooled,
and hydrochloric acid is added thereto to effect washing, followed
by filtration and then drying to obtain an unpurified
styrene-acrylic resin.
The unpurified styrene-acrylic resin obtained is dissolved in
tetrahydrofuran, and the solution thus obtained is dropwise added
to methanol to effect purification by reprecipitation. After
filtration, the product is dried to obtain the styrene-acrylic
resin.
The styrene-acrylic resin thus obtained has a glass transition
temperature (Tg) of from 54.0.degree. C., a number-average
molecular weight (Mn) of 2.0.times.10.sup.4 and a weight-average
molecular weight (Mw) of 2.0.times.10.sup.5. Styrene-acrylic resin
obtained as above (resin obtained by polymerizing 74 parts by mass
of styrene-acrylic resin and 26 parts by mass of n-butyl acrylate.
Glass transition temperature (Tg): 54.0.degree. C.; number-average
molecular weight (Mn): 20,000; weight-average molecular weight
(Mw): 200,000): 0.10 g Ester compound (or low-melting material):
0.01 g
The above materials are mixed by means of an agate mortar to
prepare a sample 1.
As a measuring instrument, "Q1000" (manufactured by TA Instruments
Japan Ltd.) or "DSC2920" (manufactured by TA Instruments Japan
Ltd.) may be used, which is a differential scanning calorimeter,
and measurement is made according to ASTM D3418-82.
For example, using "Q1000", the sample 1 is precisely weighed in an
amount of about 10 mg, which is then put in a pan made of aluminum
and an empty pan is set as reference. Using these, the endothermic
calorie is measure by the sequence shown below. The temperature at
the detecting portion of the measuring instrument is corrected on
the basis of melting points of indium and zinc, and the amount of
heat is corrected on the basis of heat of fusion of indium.
Then, the endothermic peak calorie on the second cycle is taken as
.DELTA.H1, and the endothermic peak calorie on the fourth cycle as
.DELTA.H2, and solubility is found according to the following
expression. Here, the endothermic peak calorie is defined to be the
calorie at the maximum endothermic peak in a DSC curve in the range
of temperatures of 30.degree. C. to 120.degree. C. in the course of
heating. Solubility S(%)=(1-.DELTA.H2/.DELTA.H1).times.100.
--Sequence-- First Cycle: Keeping at 30.degree. C. for 1 minute.
Heating to 60.degree. C. at a rate of 2.degree. C./minute. After
the heating, keeping for 10 minutes. Cooling to 30.degree. C. at a
rate of 10.degree. C./minute. Second Cycle: Keeping at 30.degree.
C. for 1 minute. Heating to 120.degree. C. at a rate of 10.degree.
C./minute. After the heating, keeping for 10 minutes. Cooling to
30.degree. C. at a rate of 10.degree. C./minute. Third Cycle:
Keeping at 30.degree. C. for 1 minute. Heating to 60.degree. C. at
a rate of 2.degree. C./minute. After the heating, keeping for 10
minutes. Cooling to 30.degree. C. at a rate of 10.degree.
C./minute. Fourth Cycle: Keeping at 30.degree. C. for 1 minute.
Heating to 120.degree. C. at a rate of 10.degree. C./minute. After
the heating, keeping for 10 minutes. Cooling to 30.degree. C. at a
rate of 10.degree. C./minute. Incidentally, it is preferable to use
the styrene-acrylic resin described above, but, if it is difficult
to prepare such a resin, a styrene-acrylic resin may also be used
which has a glass transition temperature of 54.0.degree.
C..+-.1.0.degree. C., a number-average molecular weight of
20,000.+-.2,000 and a weight-average molecular weight of
200,000.+-.20,000. Being within these ranges at least,
substantially the same value is obtainable for the solubility in
styrene-acrylic resin.
(6) Solubility of Ester Compound in Styrene Monomer
To 100 g of a styrene monomer kept at 40.degree. C., the ester
compound is added, and its dissolution level is found after these
have been stirred for 3 hours.
An example of an image forming apparatus in which the toner of the
present invention may favorably be used is specifically described
below with reference to the FIGURE.
In the FIGURE, reference numeral 100 denotes a photosensitive drum,
around which provided are a primary charging roller 117, a
developing assembly 140 having a developing sleeve 102, a transfer
charging roller 114, a cleaner 116, a registration roller 124 and
so forth. The photosensitive drum 100 is electrostatically charged
to, e.g., -600 V by means of the primary charging roller 117
(applied voltage: e.g., AC voltage of 1.85 kvpp and DC voltage of
-620 Vdc). Then, the photosensitive drum 100 is exposed by
irradiating it with laser light 123 by means of a laser generator
121, so that an electrostatic latent image is formed which
corresponds to the intended image. The electrostatic latent image
formed on the photosensitive drum 100 is developed with a
one-component toner by means of the developing assembly 140 to form
a toner image, and the toner image is transferred to a transfer
material by means of the transfer roller 114 brought into contact
with the photosensitive drum via the transfer material. The
transfer material holding the toner image thereon is transported to
a fixing assembly 126 by a transport belt 125, where the toner
image is fixed onto the transfer material. Some toner left on the
photosensitive drum is removed by the cleaning means 116 to clean
the surface.
An image forming apparatus of magnetic one-component jumping
development is shown here. However, the toner of the present
invention may be either of a magnetic toner and a non-magnetic
toner, and may be a toner used in any of a one-component
development system and a two-component development system. It may
further be a toner used in either method of jumping development and
contact development.
EXAMPLES
The present invention is described below in greater detail by
giving Examples and Comparative Examples, which, however, by no
means limit the present invention. In the following formulation,
"part(s)" refers to part(s) by mass in all occurrences.
Magnetic Powder Production Example
In an aqueous ferrous sulfate solution, 1.1 equivalent weight of a
sodium hydroxide solution, based on iron element, P.sub.2O.sub.5 in
an amount making 0.15% by mass in terms of phosphorus element,
based on iron element, and SiO.sub.2 in an amount making 0.50% by
mass in terms of silicon element, based on iron element, were mixed
to prepare an aqueous solution containing ferrous hydroxide.
Keeping this aqueous solution to a pH of 8.0, air was blown into
it, during which oxidation reaction was carried out at 85.degree.
C. to prepare a slurry having seed crystals.
Next, an aqueous ferrous sulfate solution was so added to this
slurry as to be 1.1 equivalent weight based on the initial alkali
quantity (sodium component of sodium hydroxide). Thereafter, the
slurry was kept to a pH of 7.6, and air was blown into it, during
which the oxidation reaction was allowed to proceed to obtain a
slurry containing a magnetic iron oxide. This slurry was filtered
and washed and thereafter this water-containing slurry was taken
out first. At this point, this water-containing sample was
collected in a small quantity to measure its water content
previously. Then, without being dried, this water-containing sample
was introduced into a different aqueous medium, and, with stirring
and at the same time with circulation of the slurry, well
re-dispersed by means of a pin mill, where the pH of the liquid
re-dispersion was adjusted to about 4.8. Then, with stirring,
n-hexyltrimethoxysilane was added thereto in an amount of 1.6 parts
by mass (the quantity of the magnetic iron oxide was calculated as
the value found when the water content was subtracted from the
water-containing sample) based on 100 parts by mass of the magnetic
iron oxide, to carry out hydrolysis. Thereafter, with thorough
stirring and at the same time with circulation of the slurry,
dispersion was carried out by means of a pin mill, and the pH of
the liquid dispersion was adjusted to 8.6, where hydrophobic
treatment was carried out. The hydrophobic magnetic powder thus
formed was filtered with a filter press, and then washed
sufficiently with a large quantity of water, followed by drying at
100.degree. C. for 15 minutes and at 90.degree. C. for 30 minutes.
The resultant particles were subjected to disintegration treatment
to obtain Magnetic Powder 1, having a volume average particle
diameter (Dv) of 0.22 .mu.m.
Production of Toner 1
Into 720 parts by mass of ion-exchanged water, 450 parts by mass of
an aqueous 0.1 mol/liter Na.sub.3PO.sub.4 solution was introduced,
followed by heating to 60.degree. C. Thereafter, 67.7 parts by mass
of an aqueous 1.0 mol/liter CaCl.sub.2 solution was added thereto
to obtain an aqueous medium containing a dispersion stabilizer.
TABLE-US-00002 Styrene 76.0 parts by mass n-Butyl acrylate 24.0
parts by mass Divinylbenzene 0.53 part by mass.sup. Iron complex of
monoazo dye (T-77, available 1.0 parts by mass from Hodogaya
Chemical Co., Ltd.) Magnetic Powder 1 90.0 parts by mass Saturated
polyester resin 5.0 parts by mass
(saturated polyester resin obtained by condensation reaction of
terephthalic acid with an ethylene oxide addition product of
bisphenol A; Mn: 5,000; acid value: 12 mgKOH/g; Tg: 68.degree.
C.)
Materials formulated as shown above were uniformly dispersed and
mixed by means of an attritor (manufactured by Mitsui Miike
Engineering Corporation). The monomer composition thus obtained was
heated to 60.degree. C., and 15 parts by mass of a paraffin wax
(melting point: 74.0.degree. C.; solubility in styrene-acrylic
resin: 2.6%) and 10 parts by mass of a behenic ester of
dipentaerythritol (hereinafter denoted "DP-622"; its physical
properties are shown in Table 1) were added thereto and mixed to
dissolve it. Thereafter, 4.5 parts by mass of a polymerization
initiator 2,2'-azobis(2,4-dimethylvaleronitrile) was dissolved to
prepare a polymerizable monomer composition.
The polymerizable monomer composition was introduced into the above
aqueous medium, followed by stirring for 10 minutes at 60.degree.
C. in an atmosphere of N.sub.2, using TK type homomixer
(manufactured by Tokushu Kika Kogyo Co., Ltd.) at 12,000 rpm to
carry out granulation. Thereafter, the granulated product obtained
was stirred with a paddle stirring blade, during which the reaction
was carried out at 70.degree. C. for 5 hours. After the reaction
was completed, the suspension formed was cooled, and hydrochloric
acid was added thereto to effect washing, followed by filtration
and then drying to obtain Toner Particles 1.
100 parts by mass of this Toner Particles 1 and 1.0 part by mass of
hydrophobic silica of 12 nm in number average primary particle
diameter were mixed by means of Henschel mixer (manufactured by
Mitsui Miike Engineering Corporation) to obtain Toner 1, having a
weight average particle diameter (D4) of 7.5 .mu.m. Physical
properties of Toner 1 are shown in Table 2.
Production of Toner 2
Toner 2 was obtained in the same way as that in Production of Toner
1 except that, in Production of Toner 1, the behenic ester of
dipentaerythritol was changed for an arachidic ester of
dipentaerythritol (hereinafter denoted "DP-620"; its physical
properties are shown in Table 1). Physical properties of Toner 2
are shown in Table 2.
Production of Toner 3
Toner 3 was obtained in the same way as that in Production of Toner
1 except that, in Production of Toner 1, the behenic ester of
dipentaerythritol was changed for a stearic ester of
dipentaerythritol (hereinafter denoted "DP-618"; its physical
properties are shown in Table 1). Physical properties of Toner 3
are shown in Table 2.
Production of Toner 4
Toner 4 was obtained in the same way as that in Production of Toner
1 except that, in Production of Toner 1, the paraffin wax having a
melting point of 74.0.degree. C. was changed for a paraffin wax
having a melting point of 83.1.degree. C. (solubility in
styrene-acrylic resin: 5.6%). Physical properties of Toner 4 are
shown in Table 2.
Production of Toner 5
Toner 5 was obtained in the same way as that in Production of Toner
1 except that, in Production of Toner 1, the paraffin wax having a
melting point of 74.0.degree. C. was changed for a paraffin wax
having a melting point of 64.2.degree. C. (solubility in
styrene-acrylic resin: 20.3%). Physical properties of Toner 5 are
shown in Table 2.
Production of Toner 6
Toner 6 was obtained in the same way as that in Production of Toner
1 except that, in Production of Toner 1, the paraffin wax having a
melting point of 74.0.degree. C. was changed for a paraffin wax
having a melting point of 87.2.degree. C. (solubility in
styrene-acrylic resin: 5.1%). Physical properties of Toner 6 are
shown in Table 2.
Production of Toner 7
Toner 7 was obtained in the same way as that in Production of Toner
1 except that, in Production of Toner 1, the amount 10 parts by
mass of the behenic ester of dipentaerythritol was changed to 2.0
parts by mass. Physical properties of Toner 7 are shown in Table
2.
Production of Toner 8
Toner 8 was obtained in the same way as that in Production of Toner
1 except that, in Production of Toner 1, the amount 10 parts by
mass of the behenic ester of dipentaerythritol was changed to 21.0
parts by mass. Physical properties of Toner 8 are shown in Table
2.
Production of Toner 9
Toner 9 was obtained in the same way as that in Production of Toner
1 except that, in Production of Toner 1, the amount 15 parts by
mass of the paraffin wax having a melting point of 74.0.degree. C.
was changed to 10 parts by mass. Physical properties of Toner 9 are
shown in Table 2.
Production of Toner 10
Toner 10 was obtained in the same way as that in Production of
Toner 1 except that, in Production of Toner 1, the amount 15 parts
by mass of the paraffin wax having a melting point of 74.0.degree.
C. was changed to 31 parts by mass. Physical properties of Toner 10
are shown in Table 2.
Production of Toner 11
Toner 11 was obtained in the same way as that in Production of
Toner 1 except that, in Production of Toner 1, the amount 0.53 part
by mass of the divinylbenzene was changed to 0.10 part by mass.
Physical properties of Toner 11 are shown in Table 2.
Production of Toner 12
Toner 12 was obtained in the same way as that in Production of
Toner 1 except that, in Production of Toner 1, the amount 0.53 part
by mass of the divinylbenzene was changed to 1.20 parts by mass.
Physical properties of Toner 12 are shown in Table 2.
Production of Toner 13
Toner 13 was obtained in the same way as that in Production of
Toner 1 except that, in Production of Toner 1, the behenic ester of
dipentaerythritol was not used. Physical properties of Toner 13 are
shown in Table 2.
Production of Toner 14
Toner 14 was obtained in the same way as that in Production of
Toner 1 except that, in Production of Toner 1, the paraffin wax
having a melting point of 74.0.degree. C. was not used. Physical
properties of Toner 14 are shown in Table 2.
Production of Toner 15
Toner 15 was obtained in the same way as that in Production of
Toner 1 except that, in Production of Toner 1, the behenic ester of
dipentaerythritol was changed for a palmitic ester of
dipentaerythritol (hereinafter denoted "DP-616"; its physical
properties are shown in Table 1). Physical properties of Toner 15
are shown in Table 2.
Production of Toner 16
Toner 16 was obtained in the same way as that in Production of
Toner 1 except that, in Production of Toner 1, the behenic ester of
dipentaerythritol was changed for a cerotic ester of
dipentaerythritol (hereinafter denoted "DP-626"; its physical
properties are shown in Table 1). Physical properties of Toner 16
are shown in Table 2.
Production of Toner 17
Toner 17 was obtained in the same way as that in Production of
Toner 1 except that, in Production of Toner 1, the behenic ester of
dipentaerythritol was changed for a stearic ester of
pentaerythritol (hereinafter denoted "PE-418"; its physical
properties are shown in Table 1). Physical properties of Toner 17
are shown in Table 2.
Production of Toner 18
Toner 18 was obtained in the same way as that in Production of
Toner 1 except that, in Production of Toner 1, the behenic ester of
dipentaerythritol was changed for hexaglycerol tetrastearate
tetrabehenate (hereinafter denoted "HG-418"; its physical
properties are shown in Table 1). Physical properties of Toner 18
are shown in Table 2.
Production of Toner 19
Toner 19 was obtained in the same way as that in Production of
Toner 1 except that, in Production of Toner 1, the paraffin wax
having a melting point of 74.0.degree. C. was changed for
Fischer-Tropsch wax having a melting point of 92.0.degree. C.
(solubility in styrene-acrylic resin: 3.8%). Physical properties of
Toner 19 are shown in Table 2.
TABLE-US-00003 TABLE 1 Physical Properties of Ester Compound
Carboxylic Solubility acid, number in styrene = Solubility Ester of
carbon Melting acrylic in styrene compound atoms point resin
monomer DP-622 22 83.degree. C. 0.5% <5.0% DP-620 20 79.degree.
C. 1.2% <5.0% DP-618 18 75.degree. C. 2.1% <5.0% DP-616 16
69.degree. C. 2.8% >5.0% DP-626 26 92.degree. C. 0.1% <5.0%
PE-418 18 76.degree. C. 4.2% >5.0% HG-418 18 64.degree. C. 8.3%
>5.0%
TABLE-US-00004 TABLE 2 Physical Properties of Toner Average Toner
particle Average THF-insoluble No. diameter circularity matter 1
7.5 .mu.m 0.971 33% 2 7.3 .mu.m 0.972 30% 3 7.2 .mu.m 0.972 34% 4
7.8 .mu.m 0.970 32% 5 7.1 .mu.m 0.972 31% 6 7.8 .mu.m 0.969 35% 7
7.1 .mu.m 0.973 37% 8 7.9 .mu.m 0.969 30% 9 7.5 .mu.m 0.971 33% 10
7.8 .mu.m 0.968 31% 11 7.6 .mu.m 0.971 4% 12 7.4 .mu.m 0.971 66% 13
7.2 .mu.m 0.972 36% 14 7.3 .mu.m 0.973 29% 15 7.3 .mu.m 0.971 36%
16 7.9 .mu.m 0.968 35% 17 7.5 .mu.m 0.972 33% 18 7.3 .mu.m 0.972
31% 19 7.9 .mu.m 0.967 36%
Example 1
Image Forming Apparatus
Using LBP-3410 (manufactured by CANON INC.; 33 sheets/minute in
A4-lengthwise paper feed) as an image forming apparatus and using
Toner 1, horizontal-line images having a print percentage of 4%
were reproduced on 6,000 sheets in a continuous mode to conduct a
running test in an environment of normal temperature and normal
humidity (23.degree. C./60% RH). A4-size 75 g/m.sup.2 sheets of
paper were used as recording mediums. As the result, neither ghost
nor fog occurred before and after the running test, and images with
a high density were obtainable. Evaluation results are shown in
Table 3.
A fixing test was also conducted in the following way.
Extra 80 g sheets of paper were used as recording mediums, and
development bias was so set that halftone images were formed in an
image density of from 0.60 to 0.65. Then, the fixing assembly was
cooled to room temperature, and heater temperature of the fixing
assembly was set (hereinafter "fixing temperature"), where, 6
seconds after electrification, a sheet with toner images was passed
through the fixing assembly to perform fixing. Thereafter, fixed
images were rubbed 10 times with Silbon paper under application of
a load of 50 g/cm.sup.2, where the rate of decrease in image
density before and after the rubbing came to 10% was regarded as
fixing start temperature. Also, on A4-size 75 g/m.sup.2 paper,
solid toner images were so formed as to be 0.6 mg/cm.sup.2 in toner
mass per unit area, and the temperature at which offset occurred at
high temperature was examined, changing the temperature of the
fixing assembly variously. High-temperature offset was observed by
visually judging the fixed images on paper, and the highest
temperature at which any high-temperature offset did not occur
(i.e., fixing end temperature) was examined. As the result, the
magnetic, Toner 1 was found to have a fixing start temperature of
180.degree. C. and a fixing end temperature of 240.degree. C.
Methods for evaluation and judgment criteria therefor are described
below on evaluations made in Examples and Comparative Examples of
the present invention.
Image Density
To evaluate image density, solid images were formed, and the
density of the solid images thus formed was measured with Macbeth
densitometer (manufactured by Gretag Macbeth Ag).
Fog
White images were reproduced, and the reflectance of the images
formed was measured with REFLECTOMETER MODEL TC-6DS, manufactured
by Tokyo Denshoku Co., Ltd. Meanwhile, the reflectance was also
measured in the same way on a transfer sheet (reference sheet)
before the white images were formed thereon. A green filter was
used as a filter. From the values of reflectance before and after
the white-image reproduction, fog was calculated according to the
following expression. Fog(reflectance)(%)=[reflectance(%) of
reference sheet]-[reflectance (%) of white-image sample].
Evaluation criteria of the fog are as follows: A: Very good (less
than 1.5%). B: Good (from 1.5% or more to less than 2.5%). C:
Average (from 2.5% or more to less than 4.0%). D: Poor (4.0% or
more).
Examples 2 to 12
The image reproduction running test and fixing text were conducted
in the same way as those in Example 1 except that Toners 2 to 12
were used, respectively. As the result, all the toners enabled
formation of images which were at least at a level of no problem in
practical use before and after the running test, and showed good
fixing performance. Evaluation results are shown in Table 3.
Comparative Examples 1 to 7
The image reproduction running test and fixing text were conducted
in the same way as those in Example 1 except that Toners 13 to 19
were used, respectively. As the result, all the toners showed a
fixing temperature of higher than 200.degree. C., resulting in an
unsatisfactory fixing performance. Also, Toners 16 and 18 caused
fog at a serious level after the running test, presumably because
of poor dispersibility of the ester compound. Evaluation results
are shown in Table 3.
TABLE-US-00005 TABLE 3 Test Results of Image Reproduction in
Low-temperature and Low-humidity Environment, and Fixing Test
Results Fixing Fixing Initial stage After running start end Image
Image temp. temp. Toner density Fog density Fog (.degree. C.)
(.degree. C.) Example: 1 1 1.53 A 1.51 A 180 240 2 2 1.52 A 1.50 A
185 240 3 3 1.49 A 1.46 B 190 240 4 4 1.50 A 1.47 B 190 240 5 5
1.47 B 1.42 B 185 240 6 6 1.49 A 1.46 B 195 245 7 7 1.54 A 1.52 A
195 240 8 8 1.45 B 1.39 B 180 240 9 9 1.53 A 1.52 A 195 240 10 10
1.44 B 1.39 C 180 240 11 11 1.51 A 1.31 C 180 200 12 12 1.53 A 1.53
A 195 250 Comparative Example: 1 13 1.52 A 1.48 A 210 240 2 14 1.53
A 1.52 A 220 240 3 15 1.48 A 1.41 B 205 240 4 16 1.41 B 1.32 D 200
240 5 17 1.38 B 1.34 C 205 240 6 18 1.35 B 1.28 D 210 240 7 19 1.37
B 1.32 C 205 240
While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is
not limited to the disclosed exemplary embodiments. The scope of
the following claims is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent structures
and functions.
This application claims priority from Japanese Patent Application
No. 2008-139237, filed on May 28, 2008, which is herein
incorporated by reference as part of this application.
* * * * *